Dear Folks,

Calculate the straight line characteristics for the following linear 1st order PDE's

1)

I calculate and when transformed becomes

but the book its given as and when transformed becomes

2)

I calculate when transformed becomes

but the book is when transformed becomes

The only way I can see them arriving at this is therefore

The pattern I see in these kind of questions is that when k is written in terms of x and y that the 'x' terms are always positve before transforming. Why is this?

Thanks